A highly sensitive, selective, and accurate spectrophotometric method for the determination of cadmium using some thiazolylazo (I-V) chromogenic reagents has been developed. In the presence of Triton X-100 and NH3/NH4Cl buffer solutions, the optimum conditions for complexation, stoichiometric ratio, and stability constants are studied. Beer's law is obeyed up to at least 4.4 μg/10 ml of cadmium. A limit of detection and quantifications of 0.96 and 3.3 ng ml−1 have been estimated and a coefficient of variation of 1.9% at the 3.0 μg level was found. The molar absorptivity and Sandell sensitivity for each reagent are calculated. The only species that interfere seriously are Hg2+ and Ni2+. The method has been applied to determine cadmium in water samples, and plant materials, and compared statistically with the AAS method. Interferences were overcome by using mixed masking agents and preliminary extraction into Aliquat 366/ carbon tetrachloride.